In an automotive engine, oil circulates between the engine, a reservoir and an oil pan. Oil is used to lubricate the engine to diminish the friction between a piston and a cylinder. A drain plug is used to seal openings in the oil pan of the engine. The oil pan generally has a tapped opening at the bottom to drain old oil from the oil pan. When removing the old oil from the oil pan, the drain plug is unscrewed to allow the old oil to drain through the tapped opening.
It is generally recommended that the engine oil of the automobile be changed every three thousand or so miles. Over a 100,000 mile span, this amounts to a maximum of about 33 oil changes. It is critical that the oil drain plug is screwed in the oil pan just right, i.e., not too tight and not too loose. If the oil drain plug is tightened too much, it may break. Also, if the oil drain plug is not screwed into the oil pan correctly, the oil pan thread may be damaged and cause oil to leak, potentially costing the automobile owner a lot of money for repairs.